This invention relates to devices for the collection and utilization of electromagnetic energy, and more particularly, to a non-imaging apparatus for solar energy collection and concentration.
The worldwide energy shortage from fossil fuels has created awareness of the need for an efficient means of utilizing energy available from other sources, and particularly, solar radiant energy. Furthermore, remote areas, such as desert outposts, may provide no readily available means for conversion of fuel to heat or electricity in efficient and controllable form.
The prior art makes numerous references to attempts at efficient solar energy utilization. The literature has generally disclosed non-focusing collectors of the flat-plate type, focusing reflectors employing curved mirror or lens surfaces, and combinations of the above. More recently, non-imaging collectors with effective solar gain have been proposed.
In general, a solar energy collector requires means for collecting the incident rays of the sun, together with means for absorbing and utilizing the collected energy. There are two types of solar energy collectors around which present-day systems are designed and built. The first form is the panel-type collector, which device comprises a flat plate, adapted to receive and direct the incident radiations to an absorbing surface, which in one embodiment carries a network of light-transparent tubing, the tubing containing a liquid flowing within, from which thermal energy can be extracted and transferred to a storage system by suitable pumps and compressors. Such panels are generally oriented to an optimal position with respect to exposure to the sun for the maximum number of hours during the year. One form of the prior art of the flatplate type is shown by Alwin B. Newton in U.S. Pat. No. 2,969,788.
A major defect of panel type collectors lies in their failure to develop high enough temperatures to permit efficient utilization of the energy converted by the collectors. Thus, the temperature of the working fluid, at most, can rise only to the level of a hot asphalt pavement on a sunny day, or about 150.degree. F. Further, where a large quantity of heat energy must be stored for future use, as to heat a residence during the night hours, a proportionately larger heat storage capacity is required, since the required quantity of heat retaining material is an inverse function of the temperature to which the material is heated.
In other prior art constructions the collection scheme employs reflective or refractive means to collect the sun's rays impinging over a relatively large area, thereafter focusing the collected energy toward a relatively small area of concentration. This approach permits obtaining very high temperatures, with a commensurate reduction in the volume of heat storage material required. However, the narrow field of acceptance of such collectors requires intricate and costly tracking apparatus to keep the sun's rays centered on the collector surface as the sun engages in its apparent diurnal motion. Such a tracking mechanism is impractical except for a research tool such as the Andorrean solar furnace, since the large mass of the moving system required where energy collection and storage is the object imposes serious practical difficulties, and sacrifices the simplicity inherent in the idea of solar energy collection.
Recent disclosures by Roland Winston, U.S. Pat. No. 4,003,638 and Riccardo Levi-Setti, U.S. Pat. No. 3,899,672, have proposed the use of so-called non-imaging light funnels of conical shape to achieve high energy concentration with minimal solar tracking. These devices have a typical concentration factor of 10, as compared with 3 or 4 for conventional non-tracking systems.
In U.S. Pat. No. 4,003,366 Daniel J. Lightfoot disclosed a solar heat system employing an elongated, triangular fluid-carrying tube, mounted within a concavo-convex reflector of hyperbolic form. However, the use of a focusing reflector without tracking means limits the energy concentration factor, as noted above.
Thus, the dichotemy between the opposing problems of solar energy concentration and solar tracking has not been resolved by the prior art. The higher cost and mechanical complexity of solar concentrators which track the sun are disadvantages which have not been overcome previously. However, as will be demonstrated, the subject invention has a capacity to concentrate incident radiant electromagnetic energy by an order of magnitude higher than the above disclosed devices, without tracking the daily motion of the sun, thus far exceeding any efficiency factor achieved by the prior art, and enabling high temperatures to be attained.